The field of the invention is effective mediate auscultation training for medical students.
The modern stethoscope is an acoustic medical device that transmits auscultatory sounds from a patient's internal organs to human ear in an air coupled manner. A flexible membrane strung over an airtight metallic bell by means of a pressure sensitive tuning mechanism which (without the vibration of the instrument itself) adds considerably to the sound. The traditional way of auscultation using a stethoscope is to press it against the skin of a patient in a very precise manner.
The proper technique to hold the instrument is key to accurate auscultation, and such technique is considered an art as well as science. Coupled with the proper location of the auscultation (pulmonary, aortic, suprasternal, tricuspid, mitral, pulmonary, or apex) the angle at which the device is held, and the pressure at which it is applied to the patient, create different airflow and dynamically modify certain properties of the instrument. This in turn causes its air column to amplify different resonant frequencies. As a result, the instrument is said to be “tuned” to different acoustic waveforms, belonging to different organs or systems.
Auscultation is spatio-temporally variant phenomena. For example the heart follows midsystolic, holosystolic (or pansystolic), early, mid and late diastolic patterns. The speed and intensity changes with the patient's condition, as well as metabolism at the time measurement was taken. The different sounds of these cycles may radiate toward cartoid arteries, apex, precordium, axilla, sternum, or none at all. The medical quality of the auscultation may be described as rumbling, blowing, harsh, rough, high-pitch, medium-pitch, low-pitch, and these may or may not be accompanied by thrill (vibrato caused by turbulent blood flow). Each of these parameters may have any of the six medically accepted intensity grades:                1. Barely audible, even to the trained ear.        2. Easily audible.        3. Equal to normal heart sound intensity.        4. Loud with palpable thrill.        5. Audible when stethoscope is in partial contact with the chest, and murmur has a palpable thrill.        6. Audible when stethoscope is over but not touching the chest, and murmur has palpable thrill.        
These qualities are of dramatic importance to a successful diagnosis. For example, a tricuspid auscultation (requires turning the chestpiece over to diaphragm side and use firm pressure) radiating towards precordium with harsh quality and high pitch may indicate the patient has a ventricular septal defect. A blowing quality instead of harsh, all else being equal, suggests the patient instead has a tricuspid insufficiency. These two different conditions produce sounds that are difficult to distinguish, even for a trained ear. The intensity grade of the auscultation can make this distinction even more difficult. Improper handling of the stethoscope over the measurement site also makes the distinction difficult. These difficulties create a risk that students might learn the incorrect sounds and associate them with wrong diagnoses.
The character of an auscultation as perceived by the human ear is controlled by the four distinct properties: pitch, loudness, timbre, and duration (time between two adjacent periods of zero loudness). Timbre is the sonic quality of a sound that defines the distinct character. For example, assume a piano, then a cello, play the same note with exactly the same loudness, duration, and pitch bend. Humans can still tell which sound came from which instrument due to the timbre. Timbre is noise invariant, and human hearing is incredibly sensitive to timbre, probably because timbre is how humans add emotion to speech. However it is dramatically less sensitive to other parameters of sound (where noise is propagated), and this sensitivity varies according to a Fletcher-Munson curve. Noise occurs principally in the pitch domain; it is a cacophony of pitched components which could end up drowning the timbre.
Loudness is how an individual perceives the volume of a sound at a certain sound pressure level. The difference between the softest and the loudest perceivable volume levels is named the dynamic range of the ear. The point where the volume is so low that the ear ceases to hear the sound is named the threshold of audibility which differs for person to person and for different pitches. In general the threshold for the higher pitches is raised when a person is getting older, until finally deafness for this pitch range occurs. Further, when the volume level is either too low or too loud for an extended period of time (such as in auscultation training sessions) more concentration is needed and the person's hearing will tire after some hours, also changing its sensitivity. It is impossible to adjust a conventional stethoscope to cope with these changes and ensure uniform loudness is heard.
In conventional patient care the experienced physician controls the stethoscope and hears the proper sounds directly. In a research hospital setting with a group of medical students to auscultate on one patient, it is impossible for the training doctor to ensure every student has heard the exact same sound mentioned in the lecture. This is because the students are yet learning how to position and hold the instrument properly. A Stethoscope is extremely sensitive to precise hand-ear coordination, and will either produce the correct sound, or a very wrong sound, or lack thereof. Further, student training requires multiple measurements which is inconvenient for the patient.
In conventional student training, one method for producing or electronic version of auscultation is to use a stethophone having electric microphones inside the ear holes to amplify the sound for play over a speaker system for simultaneous listening by students. This solution is acceptable only for very basic practice because (i) it cannot reproduce the complex low-frequency characteristics of the real instrument, (ii) the output may sound different based on the positioning and capabilities of amplifying unit as well as the shape of the room, (iii) it is prone to positive feedback from the amplifying instrument and to electrical noise from other medical and non-medical devices (e.g. fluorescent lamps), and (iv) it is a violation of patient's privacy rights since the sound is broadcast in a way it can be heard by third parties. The auscultation sounds can also be recorded for later playback to one or more students, which has the same problems. Medical students in auscultation training find themselves in a situation where the sound produced by the patient is not being heard by them at the time, location, and handling which it was produced. Instead it is heard by the experienced doctor, and described to the students verbally, who must learn to locate the same sound.
Sharing a single stethoscope is anatomically impossible since the instrument should form an air pressure barrier with both ears simultaneously lest it will not operate properly. Prior art utilizes dual-earpiece training stethoscopes for joint use by the training doctor and student, such as those sold by 3M, Mabis, and Sprague. The problem with these devices is threefold; (i) they can be used with only one student at a time. (ii), because they divide the sound and require longer tubes (2×40″ tubes versus the conventional 1×28″), wave attenuation occurs and the auscultation becomes weaker, resulting in a hearing of incorrect intensity grade. And (iii), more tubes in the way increases the risk of tubes rubbing against each other (especially if the patient is not cooperating such as in the case of children, or the room is small), which will pollute the auscultation.